Use of the global positioning system (GPS) has enabled the earth moving industry to be far more precise in constructing, for example, roads, building foundations and open mines. Global positioning system receivers, e.g., electronics capable of receiving and processing global positioning system radio signals to determine a position on the Earth, are frequently placed on earth moving equipment, for example, bull dozers, graders, plows, excavators and the like. Global positioning system receivers commonly record positions for such earth moving equipment. It is becoming more common for global positioning system receivers to guide earth moving equipment to predetermined positions. The Site Vision Automatic Grade Control System, commercially available from Trimble Navigation Limited of Sunnyvale, Calif. is an example of such systems.
A GPS system generally determines the position of the receiving antenna. As the blade of earth moving equipment is responsible for moving dirt and rocks, it is desirable to locate the antenna on the blade. Conventional GPS systems for bladed earth moving equipment generally comprise an antenna mounted on a mast, e.g., 1.5 meters in length, mounted to and rising above the earth moving blade. The mast enables improved reception of the GPS radio signals, as well as moving the antenna equipment out of the way of most debris thrown off by the earth moving operations.
The GPS receiver electronics for such systems are conventionally placed elsewhere on the earth moving equipment, for example on an engine cover or in the cab area. More specifically, in the conventional art, the GPS receiver electronics cannot be mounted on the blade attached mast, due to the extreme shock and vibration conditions of such blades.
The blades of earth moving equipment comprise one of the most violent shock and vibration environments known to man. Such blades typically endure accelerations of 50 to over 900 times the acceleration of gravity in multiple axes virtually constantly. In addition, the blades are subject to constant vibration over a wide spectrum of frequencies. Further, the mast generally contributes some multiplicative acceleration due to its length and slight bending. In general, electronic assemblies, e.g., integrated circuits and discrete components mounted on a printed circuit board, cannot survive such shock and vibration conditions. For example, integrated circuit pins can be lifted from a printed circuit board, and traces within a printed circuit board can be broken, rendering the electronic assembly non functional.
In addition, radio frequency receivers, e.g., a global positioning system receiver, typically require a highly precise and stable frequency reference. In most cases, a quartz crystal is utilized in such applications as it has desirable precision and stability characteristics. However, quartz crystals rely upon resonant mechanical movements of the crystal to achieve electrical oscillations due to the piezo-electric effect. Shock and vibration conditions common to earth moving blades can easily upset the motions of a crystal frequency reference, resulting in deleterious frequency changes or breakage, rendering the receiver inoperative.
For these reasons and others, GPS receiver electronics are conventionally not mounted to the blades of earth moving equipment. Rather, GPS receiver electronics are conventionally mounted on an engine cover or in the cab area of the earth moving equipment. A blade mounted antenna is typically coupled to receiver electronics via a radio frequency (RF) cable.
RF cabling, e.g., coaxial cable, running from a separate antenna to receiver electronics, inherently attenuates a received signal and is susceptible to induced noise. As an unfortunate consequence, received signal quality at the separated receiver is degraded from that received at the antenna and less than desired.
In addition, such RF cabling is exposed to a severe environment, including dirt, rocks and other debris flying over the top of a blade. Further, both ends of the cable, e.g., the blade mounted antenna and receiver electronics mounted elsewhere, are subject to shock and vibration, inducing a variety of mechanical stresses on such cabling. RF connectors, designed to achieve a constant impedance when coupling RF cabling to antennas and/or receiver electronics, are especially fragile. Such cabling and connector systems are subject to frequent damage, incurring not only direct repair costs, but also significant financial losses due to lack of productivity for an expensive piece of earth moving equipment and valuable operator while awaiting repair.
Thus, it has been a lot felt and unresolved need to mount global positioning system electronics directly to the blades of earth moving equipment. In addition, it is desirable to mount a receiving antenna directly to such global positioning system electronics. Further, it is desirable to meet the above-mentioned needs in a manner that is compatible and complimentary with existing designs for global positioning system electronics.